Tonepad Pulsar Rate LED? How Too?

[Wild Zebra]

  Howdy,
Just about finished the Pulsar at www.tonepad.com and was wondering
if I could get some help with installing a rate LED.  You know flashing
LEDs are way cooler. 

Thanks

[Wild Zebra]

  Getting ready to wire this up tonight.  I know, I know, there is a lot of controversy over this pedal.  However, I did not now that before I alredy had the board populated.  So, I'll cross my fingers.  My Question again is how about the rate led.  I reckon its one of the chip pins, I guess I'll just poke around.  Do I need to use this tranny type set up or just the plain ole resistor like a normal LED setup.

[no one ever]

i would like to implement a rate led in my neovibe...


that schem isn't very explanatory 

[Wild Zebra]

  That schem is for adding LEDs to a Synth so you would ignore the pin ID's.  Well I haven't got around to my pulsar yet and this topic has been skirted over twice so I guess to the ole drawing board.  I let you know if I'm successful.

[no one ever]

well i suppose that, in my case, i could hook an led up to the lamp supply line and put some big resistors to keep from blowing it?

sorry to hijack the thread.

i guess that if you study that synth and its IC's, you could find out how its sweeping the current going to the LED

[ianmgull]

I was curious if anybody ever came up with a way to implement the rate led?

[ianmgull]

Well I seem to have come up with something, not a practical method however.

I found started poking around with the meter to find wide voltage fluctuations like you would expect in a tremolo circuit. I found that right around the rate knob it would jump around between 0 and 3.5v. If you're looking at the tonepad layout:

http://tonepad.com/getFileInfo.asp?id=29

it is at the collector of Q3.

I put an LED here between the collector and ground and the LED started blinking to the pulse of the LFO. The only problem is it isn't very bright. It's a standard 5mm red from radio shack rated at 1.7v, 20ma, 3000mcd (although the back of the package says 2.4v max).

As I said, I measured the voltage fluctuations, but when I tried to measure the current at this same point I couldn't get a reading for some reason. I put my meter on the same node and touched the other probe to ground and got nothing. Now I embarrassingly don't know as much about Ohm's Law as I should, but is this even possible???

Am I on the right track?

Would a simple boost circuit work to get the LED up to a reasonable brightness? 

 

[ianmgull]

Last one for tonight, I promise 


So I was looking at other schematics for tremolos with rate LED's and I thought that R20 (on the tonepad layout) was simultaneously acting as a current limiting resistor for the LED as well as in some way biasing Q3.  I replaced the stock 47k resistor for a 22k.

Bingo! LED gets brighter but now there is another problem: the minimum speed of the LFO almost doubles.

I'm starting to see that this is going to be a balancing act. If anyone has any idea's I would love to hear them.

Thanks.

[oskar]

Come on guys! The transistor needed to drive the rate LED is going to do the same job as Q1
It would have to look something like this...       
I took the values out of thin air though.

[ianmgull]

Come on guys! The transistor needed to drive the rate LED is going to do the same job as Q1
It would have to look something like this...       
I took the values out of thin air though.

hmmm... I guess I just assumed putting a diode directly in the LFO path would have a negitive impact. Also, I assume you're talking about Q3 in the schem and not Q1? I'll try it when I get home and see what happens. So does a diode have significant resistance itself? I'm slightly confused about the theory here.

[oskar]

So does a diode have significant resistance itself?

None. It's magic powers is dropping the voltage. It simply makes voltage dissappear.   

I'm slightly confused about the theory here.

Don't dig any further. It will only give you nightmares.
But find out for yourself--->   Horror!

Also, I assume you're talking about Q3 in the schem and not Q1? I'll try it when I get home and see what happens. So does a diode have significant resistance itself? I'm slightly confused about the theory here.

Q1 on my drawing refers to my drawing only. It would become Q4 on the new "blinkenlicht übermod pulsar" and connect to Q2 collector
on the Tonepad schematic. Start out with R1/100k and R2/1k. The transistor can be just any NPN.
Basically an LED needs some current to light up and if you take it from the LFO it's diverting current from it's main duty.

I hate diods, and don't get me started on transistors...

[ianmgull]

hahaha I see what you're saying now oskar.

So I need a separate transistor circuit to boost the current for the LED. I'll perf this up tonight and let you guys know how it goes. Thanks!

[oskar]

Q2 out is a pulse so if you want the LED to follow the amplitude you'ld have to tap into R12/R13 junction.
Make R1 bigger. 470k...  this then will pull down the voltage on C7/C6 so you have to lower R13 to 120k.
   I'm learning Spice simulation. So these values are according to Pulsar LFO according to switchercad.

Happy breadboarding!
( you posted while I was writing. )

[ianmgull]

It works!!!!

I connected the base of what is now Q4 to the junction of R12/R13 through a 100k resistor, grounded the emitter, and connected the LED to the collector through a 1k resistor. I ended up using a 2n3904 with no problems. I've got it on the breadboard right now but I plan on putting it in a box with a light emitting boarder. Thanks a lot oskar!!!!!!

Ian

[oskar]

At last, years of research     
Any volume drop?

[ianmgull]

Not any noticeable one, although I was on a breadboard, through a bench amp, with less than perfect conditions. I'll get it boxed up and in working order and then report back. Thanks again.

[chromesphere]

Did this pulsating LED mod as shown above by Oskar, and can confirm that it does work.  I can not tell any difference in tone.

(Thanks Oskar!)

CS

[jacobyjd]

That's the same application I used in my Gristleizer, and that which is built into the boards Taylor had made for the project. It's crude, but it works, since the LED's path to GND is hijacked by the transistor. The LFO conveniently switches the transistor at its frequency

[tasos]

it is at the collector of Q3.

it is not!it is the collector of q2!i just tried that and i get super brightness with a 5mm red led!!!and here is something even cooler!when i connect the led there is a fastest tremolo!this is awesome!try that!

[Scruffie]

it is at the collector of Q3.

it is not!it is the collector of q2!i just tried that and i get super brightness with a 5mm red led!!!and here is something even cooler!when i connect the led there is a fastest tremolo!this is awesome!try that!

I think you need to read the rest of the thread, even just his post, he says it's not particularly pratical and also... later on discovers the correct way to do this... plus this thread is nearly 2 years old!

This Circuit-


And This -

Q1 on my drawing refers to my drawing only. It would become Q4 on the new "blinkenlicht übermod pulsar" and connect to Q2 collector
on the Tonepad schematic. Start out with R1/100k and R2/1k. The transistor can be just any NPN.
Basically an LED needs some current to light up and if you take it from the LFO it's diverting current from it's main duty.

Are The Correct Answers and Verified Twice in This Thread by both the poster who mentioned Q3 and another Party.